448 Mr. A. Essex's Account of the 



ment for the use of my brother Mr. William Essex, Painter in 

 Enamel to H. R. H. the Princess Augusta. One of the objects 

 which I have endeavoured to accomplish, and in which I have 

 not been unsuccessful, is, that they should be of the same co- 

 lour when on the palette as they will be when they have passed 

 through the fire. The colours possessing this property, the 

 artist is enabled to see while proceeding with his wor-k, the 

 precise effect that will be produced after the painting has un- 

 dergone fusion. Thus the power of attaining greater preci- 

 sion in imitating the original is secured. 



In Brongniart's " Essay on the colours obtained from the 

 metallic oxides and fixed by fusion on different vitreous bodies," 

 which has been before quoted, it is observed that oxides "which 

 adhere little to the great quantity of oxygen they contain, can- 

 not be employed The colour they present cannot be de- 

 pended on, since they must lose it in the slightest heat by 

 losing a part of their oxygen." This assertion looks very 

 well in theory, but I confess I was surprised to find such a 

 statement put forth by an able practitioner. In his paper on the 

 black oxide of platinum*, Mr. Cooper observes, "A curious 

 property of this oxide should here be mentioned. When 

 heated per se, or with combustibles, it is easily reduced, but 

 when mixed with enameller's flux, it is capable of sustaining 

 a very intense heat, without decomposition ; indeed it has with- 

 stood reduction in the most violent degree of heat I was able 

 to give it." To this may be added, that no colours are more 

 to be depended upon, more indestructible in the fire, than 

 those prepared from the oxides of platinum and of gold; and 

 yet of the oxides of these metals it may be said, in the lan- 

 guage of M. Brongniart, that they above all others " adhere 

 little to the oxygen they contain," they standing lowest among 

 the metals for affinity for oxygen f . 



Ever}^ person at all acquainted with the receipts for enamels, 

 as framed by those who had not that light to guide them which 

 is afforded by modern chemistry, must be aware of the strange 

 jumble which they almost universally present. Feeling certain 

 that here, as in every other instance in which excellence is 

 sought, simplicity was desirable, I have kept the attainment of 



* Journal of the Royal Institution, vol. iii. p.. 121. 



t See a paper by V. Regnault in the Number for August, 1836, of the 

 Annates de Chimie et de Physique, which appears to give the latest results on 

 this subject. I am aware that it is conceived by Prof. Proust and others 

 that the gold in the powder of Cassius, (which is employed to produce a 

 purple colour in enamel,) is not in the state of oxide. Various considera- 

 tions, however, have led me to a different conchision, and I am much 

 pleased to find that I am supported in this opinion by authority so eminent 

 as that of the late Dr. Turner. See his Elements of Chemistry, Fifth Edi- 

 tion, p. 645. 



